1. Field of the Invention
This invention relates to a filter device, and more particularly to a filter cartridge which is used in a liquid or gas filter. Still more particularly, the present invention relates to a filter cartridge which employs granulated material such as activated carbon as a filtering material. Such filters are typically used with aquariums.
2. Description of the Prior Art
A prior art filter cartridge is illustrated in FIGS. 1 and 2. Such filter includes a central plastic stiffener 10 to which is attached a pair of porous filter elements 12 and 14. Typically, the filter elements are secured to the periphery of the stiffener by means of heat, sonic, radio-wave, chemical, or mechanical attachment. The stiffener serves to maintain the shape of the filter elements.
In order to increase filtration efficiency, granules 16 of filter media, such as activated carbon, are carried within the space between the filter elements 12 and 14. In use, the filter cartridge is maintained in a vertical or semi-vertical orientation. Because of the relative flexibility of the filter elements 12 and 14, the granules tend to fall toward the bottom of the filter cartridge as illustrated in FIG. 2. Water passing through the upper portion of the cartridge thus does not receive any granular filtration and overall filtration efficiency is reduced.
The manufacturing process for the prior art structure is a three step procedure which involves initially attaching one of the filter elements to the stiffener, subsequently spreading carbon granules over the surface of the filter element (while maintaining the element horizontal), and finally attaching the second filter element to the stiffener to thereby secure the carbon between the two filter elements.